6.6 Duramax Diesel Problems (Things to Know)

The 6.6 Duramax, also known as the LB7, is an iconic engine that set a standard for quality and longevity which, frankly, GM has not been able to match in subsequent engines. Does this beast of an engine have problems though? Well, that’s what we will e exploring in this article.

Capable of lasting well over 500,000 miles with a few owners reporting mileages close to a million miles, the 6.6 Duramax stands in a class of its own among American truck engines. Even though it stands head and shoulders above others, it does a few notable problems associated with it.

What are Common 6.6 Diesel Duramax Problems?

The one most commonly reported issue that arose early on in its history was fuel injector failure. This was due to the fact that they moved from mechanical to electronic injectors.

They were supposed to be a lot more efficient and economical, injecting the right amount of fuel at the right time. While this initially delivered on what it was designed to do, some failures began to occur leading to some complications.

This ultimately led to a recall of all vehicles with the first generation engine. The injectors were replaced with ones that managed to deliver the desired results but also lasted longer. The following are other common problems with the 6.6 Duramax reported over several generations of the engine:

Water Pump Failure:

This problem was most commonly reported in the LLY and LB7 series that came out between 2004 and 2005. To fix this problem, a larger water pump was designed and fitted in the 2006 model.

The earlier version of the water pump would usually fail at the 75,000-mile mark. After this replacement, the water pump issue stopped occurring in the 6.6 Duramax.

Head Gasket Blowing, Overheating Engine, and High Coolant Temperatures:

Several issues occurred related to the engine temperature. This problem is common in the 2005 model and earlier versions. The engine would overheat when the truck towed during the hot summer months.

To fix this problem, a larger radiator and, as already stated earlier, a bigger water pump were put in starting from 2006.

Glow Plug Failure and Tips Breaking:

This particular problem affected the LBZ and LLY engines from 2006. Faulty glow plug modules resulted in an unusually high rate of glow plug failure.

Glow plugs were reported to get brittle and in some cases, break while the engine was running. When this happened, catastrophic engine failure was often the result. GM had to recall the affected model years and fix the problem.

Clogged DPF:

This problem affected the LML and LMM 6.6 Duramax engines. The problem was eventually dealt with when GM introduced the selective catalytic reduction system. Before this happened, however, there would be significant numbers of cases where ash and soot would build up in the DPF over time. DPF clogging resulted in low-performance level, high levels of smoke, rough idling as well reduced fuel efficiency.

Is the 6.6 Litre Duramax a Good Engine?

Despite all the problems listed above, the 6.6 Litre Duramax stands out as one of the best diesel truck engines ever. At the low end, you can expect to get a lifespan of around 300,000 to 500,000 miles.

With good maintenance, the engine is capable of going well over the 500,000mile mark with some recorded at close to 1 million miles. That’s a great track record by any measure.

The 6.6 Duramax engine is superb. It offers considerable power, reliability, and performance. It is arguably one of the best, if not the best truck engine ever to come from American car manufacturers.

What Year Did the 6.6 Duramax Have Problems?

When it comes to answering this question, it does somewhat feel like you are pulling at straws. The Duramax is a great engine with a great track record.

Outside of the issues mentioned in this post, there really isn’t much to dislike about this engine. However, if you are to look at which 6.6 Duramax years will have the highest probability of problems, we would have to give a broad answer and say year 2001 to 2010 are the ones you need to stay away from.

How Many Miles Should a 6.6 Duramax Last?

The Duramax engine is reliable and durable. When properly taken care of the engine lasts a modest 300,000 miles of service. At 200,000 miles, the engine requires changes of water pumps and other essential aspects of the engine. Consumers have denoted that, their trucks have sustained a range of 500 000 miles of service.


The 6.6 Duramax engine is a marvel of engineering. Most of the issues labeled against the engines can be easily dealt with, making the engine one of the most reliable and high-performing trucks.